Chesterfield County may by ordinance provide that the county may use public funds to repair existing residential dwellings damaged by foundation failures caused by high clay content soil subject to moisture-related shrinking and swelling. Such ordinance may place conditions on the use or expenditure of such public funds. The expenditure of such public funds by the county under this section during a fiscal year shall not exceed two percent of the county’s locally derived revenues from that fiscal year. For purposes of this section, “public funds” includes only general tax revenues from real and personal property and does not include any special fee assessment, or other tax or charge, however denominated. The county shall keep funds collected for building permit fees and any funds received from any other fees collected under any special act in separate accounts, and separate from other locally derived revenues, and may not use fees collected for building permits or fees collected under any special act, directly or indirectly, for purposes authorized under this section.